It is well known that upon the color development of a silver halide photographic light-sensitive material, after exposure, an oxidized aromatic primary amine developing agent can be reacted with a dye forming coupler to obtain a color image.
It is also known that, for the color development of a silver halide color photogrpahic material, an oxidized aromatic primary amine color developing agent can be reacted with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine, and the like, thus forming a color image. In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green and red light, and yellow, magenta and cyan color image formers, which are respectively the complementary colors of blue, green and red, are employed. For example, a coupler of the acylacetanilide or benzoylmethane type is used for forming a yellow color image; a coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type is generally used for forming a magenta color image; and a phenolic coupler, such as a phenol and a naphthol, is generally used for forming a cyan color image.
Color couplers must satisfy various requirements. For example, it is necessary that they have a good spectral property and provide a dye image having excellent stability to light, temperature, and humidity for a long period of time upon color development.
It is also required in a multilayer color photographic light-sensitive material that each coupler is fixed in a layer separated from each other in order to reduce color mixing and improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method is to introduce a long chain aliphatic group into a coupler molecule in order to prevent diffusion. Couplers according to such a method require a step of addition to an aqueous gelatin solution by solubilizing in alkali, or a step of dispersing in an aqueous gelatin solution by dissolving in a high boiling organic solvent, since the couplers are immiscible with an aqueous gelatin solution. Such color couplers may cause crystal formation in a photographic emulsion. Furthermore, when using a high boiling organic solvent, a large amount of gelatin must be employed since the high boiling organic solvent makes an emulsion layer soft. Consequently, this increases the thickness of the material even though it is desirable to reduce the thickness of the emulsion layer.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler obtained by polymerization of a monomeric coupler in a latex form. An example of a method of adding a polymer coupler in a latex form to a hydrophilic colloid composition is a method in which a latex prepared by an emulsion polymerization method is directly added to a gelatino silver halide emulsion and a method in which an oleophilic polymer coupler obtained by polymerization of a monomeric coupler is dispersed in a latex form in an aqueous gelatin solution. Some examples of the former emulsion polymerization methods include an emulsion polymerization method in an aqueous gelatin phase as described in U.S. Pat. No. 3,370,952 and an emulsion polymerization method in water as described in U.S. Pat. No. 4,080,211. An example of the latter method in which an oleophilic polymer coupler is dispersed in a latex form is described in U.S. Pat. No. 3,451,820.
The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. For example, the deterioration of strength of the film formed is small, because the hydrophobic substance is in a latex form. Also, since the latex can contain coupler monomers in a high concentration, it is easy to incorporate couplers in a high concentration into a photogrpahic emulsion. Further, the film can be thinned since the increase in viscosity is small and, thereby, sharpness can be improved. Furthermore, color mixing is prevented, since a polymer coupler is completely immobilized and the crystallization of couplers in the emulsion layer is small.
With respect to the addition of these polymer couplers in a latex form to a gelatino silver halide emulsion, there are described, for example, 4-equivalent magenta polymer coupler latexes and methods of preparation thereof in U.S. Pat. No. 4,080,211, British Pat. No. 1,247,688, and U.S. Pat. No. 3,451,820, copolymer latexes with a competing coupler in West German Patent No. 2,725,591, and U.S. Pat. No. 3,926,436 and cyan polymer coupler latexes in U.S. Pat. No. 3,767,412 and Research Disclosure, No. 21728 (1982).
However, these cyan polymer coupler in a latex form have the following problems to be dissolved as well as many excellent features as described above, and thus it has been desired to overcome these problems. In particular, improvement in fastness to heat is strongly desired.
1. In a color photograph after development, the fastness to heat and wet heat of the cyan color image is low.
2. As the reaction rate of coupling is poor, the sensitivity, gradation and color density of the dye image formed are low.
Research Disclosure 21728 (1982) shows that in a latex having a grain size of 0.1 .mu.m or less which is obtained by emulsion polymerization, the fastness to heat and wet heat can be improved by copolymerizing a cyan color image-forming monomer coupler with acrylic acid or methacrylic acid, but the color forming property is insufficient and further improvement is desired.